1. Field of the Disclosure
The present invention relates to a driving method of a liquid crystal display device, and more particularly, to a black-data insertion driving method of a liquid crystal display device that improves brightness differences in an upper portion and middle/lower portions of a display panel.
2. Discussion of the Related Art
Recently, to improve image qualities and visual properties, various driving methods of a liquid crystal display (LCD) device have been suggested, and a black-data insertion driving method has been used as one of those driving methods.
FIG. 1 is a view of schematically illustrating an LCD device for a black-data insertion driving method according to the related art. FIG. 1 shows a liquid crystal panel 10, a timing control unit 20, a source driving unit 30, and a gate driving unit 40.
Referring to FIG. 2, which is a view of schematically illustrating a liquid crystal panel of FIG. 1, the liquid crystal panel 10 includes gate lines GL1 to GLn and data lines DL1 to DLm, which are formed on a substrate such as a glass substrate and cross each other to define pixel regions. A thin film transistor TFT and a liquid crystal capacitor CLC are formed at each pixel region, whereby an image is displayed by applied data through the pixel regions.
The timing control unit 20 may be referred to as a timing controller. The timing control unit 20 receives control signals and clock signals (CLKs) from the outer driving system such as TV or graphic cards and generates control signals for driving the source driving unit 30 and the gate driving unit 40. In addition, the timing control unit 20 provides RGB image data from the outer driving system to the source driving unit 30.
The source driving unit 30 includes a plurality of source drive integrated circuits, and the gate driving unit 40 includes a plurality of gate drive integrated circuits. The source driving unit 30 receives a plurality of gamma reference voltages and selects gamma reference voltages corresponding to the image data, responding the control signals inputted from the timing control unit 20. The source driving unit 30 generates data voltages Vdata according to the selected gamma reference voltages and provides the data voltages Vdata to the liquid crystal panel 2 to control rotation angles of liquid crystal molecules.
The gate driving unit 40 outputs gate driving signals Vg for controlling on/off of the thin film transistors TFTs arranged on the liquid crystal panel 10, responding the clock signals CLKs and the control signal inputted from the timing control unit 20. By sequentially enabling the gate lines GL1 to GLn on the liquid crystal panel 10, the thin film transistors TFTs on the liquid crystal panel 10 are sequentially driven line by line, and analog image signals from the source driving unit 30 are inputted to the pixels connected to the thin film transistors TFTs.
The gate driving signals Vg outputted from the gate driving unit 40, beneficially, are classified into an image-data gate driving signal Vg_D for inputting the image data and a black-data gate driving signal Vg_B for inputting black data. To do this, the gate driving unit 40 may be divided into an image-data gate driving unit and a black-data gate driving unit.
Referring to FIG. 3, a black-data insertion (BDI) driving method is to improve image qualities and visual properties of displayed images by defining a black area BA for inputting black data in a display area and moving the black area in the display area every frame.
FIG. 4 is a timing diagram of input data for explaining a black-data insertion (BDI) driving method according to the related art. FIG. 4 shows input timings of image data ID and black data BD at an (n−1)th frame and at an nth frame.
In FIG. 4, the image data ID is inputted with a positive (+) polarity at the (n−1)th frame and then is inputted with a negative (−) polarity at the nth frame due to a polarity inversion. The black data BD is inputted with a negative (−) polarity at the (n−1)th frame and then is inputted with a positive (+) polarity at the nth frame due to the polarity inversion.
Here, symbols t1, t2, t3 designate a blank interval of the image-data gate driving signal Vg_D, a blank interval of the black-data gate driving signal Vg_B, and a pattern change timing of a polarity inversion signal.
In the timing diagram, the black data BD of the negative (−) polarity is inputted to an upper portion of a display panel, which corresponds to an interval t4, at the end of the (n−1)th frame. Then, the image data ID of the negative (−) polarity is sequentially inputted from an upper portion of the display panel at the nth frame.
By the way, when the image data ID is inputted at the nth frame, the upper portion of the display panel, which corresponds to an interval t6, is the same as the upper portion of the display panel corresponding to the interval t4. The black data BD of the negative (−) polarity is inputted to the upper portion of the display panel at the (n−1)th frame, and the image data ID of the negative (−) polarity is inputted to the upper portion of the display panel at the nth frame. Accordingly, voltages of the same polarity are sequentially charged to the pixels, and this is a “strong” charge condition.
On the other hand, subsequently, the black data BD of the positive (+) polarity is inputted to an area corresponding to an interval t5, and then the image data ID of the negative (−) polarity is inputted to an area corresponding to an interval t7, which is the same as the area corresponding to the interval t5. Accordingly, voltages of different polarities are sequentially charges to the pixels, and this is a “weak” charge condition.
More particularly, the upper portion of the display panel, where the image data ID is inputted at the nth frame, has a “strong” charge condition due to the black data BD of the same polarity previously inputted, and other portions, that is, middle/lower portions of the display panel has a “weak” charge condition because the image data ID is inputted with the polarity opposite to the black data BD previously inputted. Therefore, The upper portion and the middle/lower portions of the display panel have a difference in brightness of a display image.
The brightness difference is caused by a change of signal levels of the polarity inversion signal, which is provided to the source driving unit 30 of FIG. 1 and enables an inversion driving. Referring to FIG. 5 showing signal level patterns of the polarity inversion signal POL, the pattern of the polarity inversion signal POL at the (n−1)th frame is inverted at the nth frame for the inversion driving. At this time, a pattern change point t3 of the polarity inversion signal POL is disposed in a section of outputting the back data gate driving signal Vg_B. Thus, since the black data BD and the image data ID are inputted with opposite polarities in the middle/lower portions of the display panel, the brightness difference is caused due to the “weak” charge of the image data ID.